The articular cartilage, or “hyaline cartilage”, of healthy vertebrates (including humans and other mammals) is a semi-transparent, opalescent connective tissue characterized by a columnar growth pattern of chondrocytes in an extracellular matrix (ECM) composed predominantly of proteoglycans, type II collagen, and water. Articular cartilage provides an effective weight-bearing cushion to prevent contact between opposing bones in a joint and thus is critical to the normal function of the joint. Articular cartilage is not only susceptible to damage by joint trauma, but also to a gradual process of erosion. Initially, such an erosion may be simply an asymptomatic “partial thickness defect” in which an area of reduced hyaline cartilage does not penetrate completely to the subchondral bone. Such partial thickness defects are usually not painful and typically are only detected during arthroscopic examination. However, if the erosive process is not treated, the base of a partial thickness defect may continue to wear away and the diameter of the defect may increase such that the defect eventually progresses to a “full thickness defect” that penetrates the underlying bone. Such full thickness defects may become sufficiently large that surfaces of opposing bones of the joint make contact and begin to erode one another, leading to inflammation, pain, and other degenerative changes, i.e., the classic symptoms of osteoarthritis (OA). Osteoarthritis is thus a degenerative, progressive, and crippling disease that results in joint deformity, instability, impairment, and pain. Eventually, joint replacement surgery may be the only practical recourse for restoring, at least in part, some level of mobility to an individual.
The IL-1 superfamily is comprised of mediators of inflammatory processes with a wide range of biological and physiological effects, including fever, prostaglandin synthesis (m, e.g., fibroblasts, muscle cells and endothelial cells), T-lymphocyte activation, and interleukin-2 production. The original members of the IL-1 superfamily are IL-1α, IL-1β, and the IL-1 Receptor Antagonist (IL-1Ra, IL-1RA, IL-1ra, IL-1Rα). IL-1α and IL-β are pro-inflammatory cytokines involved in immune defense against infection. The IL-1Rα competes for receptor binding with IL-1α and IL-1β, blocking their role in immune activation. Other members of the IL-1 superfamily include IL-18 (see Dinarello (1994) FASEB J. 8(15):1314-1325; Huising et al. (2004) Dev. Comp. Immunol. 28(5):395-413) and six additional genes with structural homology to IL-1α, IL-1β, or IL-1RA, named IL1F5, IL1F6, IL1F7, IL1F8, IL1F9, and IL1F10. In accordance, IL-1α, IL-1β, and IL-1RA have been renamed IL-1F1, IL-1F2, and IL-1F3, respectively (see Sims et al. (2001) Trends Immunol. 22(10):536-537; Dunn et al. (2001) Trends Immunol. 22(10):533-536). A further putative member of the IL-1 family has been described called IL-33 or IL-1F11, although this name is not officially accepted in the HGNC gene family nomenclature database.
Both IL-1α and IL-1β are produced by macrophages, monocytes, and dendritic cells. They form an important part of the inflammatory response of the body against infection. These cytokines increase the expression of adhesion factors on endothelial cells to enable transmigration of leukocytes to sites of infection and re-set the hypothalamus thermoregulatory center, leading to an increased body temperature which expresses itself as fever. IL-1 is therefore called an endogenous pyrogen. The increased body temperature helps the body's immune system to fight infection. IL-1 is also important in the regulation of hematopoiesis. IL-1β production in peripheral tissue has also been associated with hyperalgesia (increased sensitivity to pain) associated with fever (Morgan et al. (2004) Brain Res. 1022(1-2):96-100). IL-1 upregulates expression of cyclooxygenase-2 (COX-2) associated with pain. For the most part, IL-1α and IL-1β bind to the same cellular receptor. This receptor is composed of two related, but non-identical, subunits that transmit intracellular signals via a pathway that is shared in large part with certain other receptors. These include the Toll family of innate immune receptors and the IL-18 receptor. IL-1α and IL-1β also possess similar biological properties, including induction of fever, slow wave sleep, and neutrophilia, T- and B-lymphocyte activation, fibroblast proliferation, cytotoxicity for certain cells, induction of collagenases, synthesis of hepatic acute phase proteins, and increased production of colony stimulating factors and collagen.
cDNAs encoding IL-1α and IL-1β have been isolated and expressed; these cDNAs represent two different gene products, termed IL-1α (Lomedico et al. (1984) Nature 312:458) and IL-1β (Auron et al. (1984) Proc. Natl. Acad. Sci. USA 81:7909). Eight interleukin 1 family genes form a cytokine gene cluster on chromosome 2. IL-1β is the predominant form produced by human monocytes both at the mRNA and protein levels. The two forms of human IL-1 share only 26% amino acid homology. Despite their distinct polypeptide sequences, the two forms of IL-1 have structural similarities (Auron et al. (1985) J. Mol. Cell. Immunol. 2:169), in that the amino acid homology is confined to discrete regions of the IL-1 molecule.
IL-1α and IL-1β are produced as precursor peptides. In other words they are made as a long protein that is then processed to release a shorter, active molecule, which is called the mature protein. IL-1α is produced as a proprotein that is proteolytically processed by calpain and released in a mechanism that is still not well studied. Mature IL-1β, for example, is released from Pro-IL-1β following cleavage by a certain member of the caspase family of proteins, called caspase-1 or the interleukin-1 converting enzyme (ICE). The 3-dimensional structure of the mature forms of each member of the human IL-1 superfamily is composed of 12-14 β-strands producing a barrel-shaped protein.
IL-1α was originally termed “catabolin” because of its effect in increasing cartilage resorption, but also as “monocyte cell factor” (MCF) because of its stimulatory effect on collagenase and prostaglandin in synovial cells, and as “leukocyte endogenous factor” (LEM) having a stimulatory effect on acute phase reactions. IL-1α has a broad spectrum of biological activities, since IL-1α is synthesized by many different cells, such as monocytes, macrophages, fibroblasts, endothelial cells and lymphocytes, and many cells possess specific receptors for IL-1α. IL-1α stimulates thymocyte proliferation by inducing IL-2 release, B-cell maturation and proliferation, and fibroblast growth factor activity. IL-1α proteins were identified as endogenous pyrogens and are reported to stimulate the release of prostaglandin and collagenase from synovial cells. Thus, IL-1α also occupies a central position as the trigger for various disorders and symptoms of disorders. These disorders are often predominantly serious disorders for which there is little or no treatment. It has been suggested that the polymorphism of these genes is associated with rheumatoid arthritis and Alzheimer's disease. IL-1 in general has been implicated in many human diseases, including arthritis, pulmonary fibrosis, diseases of the central nervous system, diabetes mellitus, and certain cardiovascular diseases. The undesirable effects of IL-1α are described in, for example, Oppenheim et al. (1986) Immunol. Today 7:45-56, Durum et al. (1985) Ann. Rev. Immunol. 3:263-287 and Symons et al. (1989) Lymphokine Res. 8:365-372.
The initiation, maintenance, and progression of OA is mediated by a complex cascade of mechanical and biochemical pathways in which IL-1 plays a pivotal role. IL-1α and IL-1β are produced not only by monocytes, macrophages, and neutrophils, but by cells in joint tissues, such as chondrocytes, synovial fibroblasts, and osteoclasts (see, e.g., Dinarello et al. (2009) Ann. Rev. Immunol. 27: 519-550). In vitro, IL-1 can stimulate chondrocytes and synoviocytes to produce proteinases involved in cartilage destruction leading to OA (see, e.g., Dayer et al. (1977) Science 195: 181-183; Dayer et al. (1984) Biochem. Pharmacol. 33: 2893-2899; McGuire-Goldring et al. (1984) Arthritis Rheum. 27: 654-662), as well as inhibit synthesis of proteoglycan and collagen type II, the main components of the extracellular matrix (ECM) of normal hyaline cartilage (see, e.g., Goldring et al. (1987) J. Biol. Chem. 262: 16724-16729; Goldring et al. (1988) J. Clin. Investig. 82: 2026-2037). Preclinical and clinical studies have provided further evidence of IL-1 in the pathogenesis of OA. For example, intra-articular (ia) injection of IL-1 into animal knees resulted in leukocyte infiltration and cartilage loss (Pettiphar et al. (1986) Proc. Natl. Acad. Sci. USA 83: 8749-8753). In contrast, ia injection of IL-1 antagonist resulted in significant reduction in the progression of experimental OA (see, e.g., Pelletier et al. (1997) Arthritis Rheum. 40: 1012-1019; Caron et al. (1996) Arthritis Rheum. 39: 1535-1544); Fernandes et al. (1999) Am. J. Pathol. 154: 11590-11690); Zhang et al. (2006) Biochem. Biophys. Res. Commun 341: 202-208). In addition, IL-1 knockout (KO) mice were found to be resistant to surgically induced cartilage damage when compared to their wild-type counterparts (Glasson et al. (2009) Osteoarthritis Cartilage, 18: 572-580).
Both IL-1α and IL-1β are expressed in synovial membranes, cartilage, and synovial fluid of human OA patients (see, e.g., Farahat et al. (1993) Ann. Rheum. Dis. 52: 870-875). The IL-1 antagonist, Anakinra, which is an IL-1 receptor antagonist, and AMG-108, which is an IL-1 receptor monoclonal antibody, have demonstrated some efficacy in OA trials with respect to symptoms and chondroprotection (“Results from a Randomized Controlled Trial of AMG 108 (a fully human monoclonal antibody to IL-1R type 1) in Patients With Osteoarthritis of the Knee” Cohen et al., ACR 2007). Both of these proposed therapies await additional studies to demonstrate clear and robust clinical efficacy.
A need remains for new and effective methods and compositions for treating individuals afflicted with osteoarthritis.